Need advice for insulated MCH mounting on PCB

[pvit]

I'd like to make micro-reflow device for hobby, and the most difficult is to invent how to mount MCH heater on PCB and protect PCB from heating. Of cause, solution should be simple & easy to repeat by anyone.

First attempt was to use "chineese aerohel" from aliexpress. It's not convenient material (too many dust), and insulation is far from ideal. Also, it causes too slow cooldown.

Second attempt was to use air space and reflector. Since bottom convection is very low, we should mostly care about IR waves.



Heater sits on cone bolts in brass insets. Physical contact is very  small. Base PCB is covered with "acrylic glass" film for bathrooms .

Better, but still not enougth. On the way - additional cover of heater bottom with reflective paint (i'm waiting until paint dries, but preliminary result is very impressive). Then, will try to make separate reflective surfacebetween PCB and MCH.

Question 1.

Do you have ideas how to mount MCH on PCB with good thermal insulation and low height?

Question 2.

Since i need equal temperature on all surface, about 10mm of plate from each side become useless (checked by thermal imager). Only 30x30mm left. Not bad, but i'd like to improve.

Idea is to attach Panasonic PGS sheet on top. Can you advice glue for that? Ideally, with up to 400C operating temperature, available on aliexpress or ebay. If that's impossible - up to 300C.

[jhpadjustable]

I'd put air space between the reflector and the board, perhaps by adding a square of whatever sheet metal is to hand, drilled to sit between the board and another, shorter set of threaded spacers. Then again, I'm more inclined to build a mini-oven than a mini-hot plate.

[pvit]

I'd put air space between the reflector and the board, perhaps by adding a square of whatever sheet metal is to hand, drilled to sit between the board and another, shorter set of threaded spacers.

Yes, mentioned that in first post. I think the most simple will be to use one more PCB and apply aluminium adhesive tape.

Then again, I'm more inclined to build a mini-oven than a mini-hot plate.

It will not be micro and easy-to-do then. Current device is targeted very carefully. It's for hobbyists like me, who assemble pcb-s 1-2 times per year and have no room/need for "better tools".

[pvit]

It was bad idea to use acrylic mirror in reflector. After change to aluminium tape, result improved significantly. 25 min, 180-190C, PCB temperature ~ 40-50C.

Seems may work without intermediate surface.

[pvit]

After lot of experiments, found useable combination:





Mounting consists of M2 SS screws, sharpened to cones on the ends + 2 nuts (one at each PCB side). Can work many hours with top 260C, and keep PCB only a bit warm. Hottest spots are screw heads, only 45C. Interval between PCB and MCH = 10mm.

While current result is already useable, plan switch from M2 to M1.6 in real project. With doubled reserve, will try 2 more optimizations:

- try not sharpened screws (more easy to assemble)
- try reduce interval between MCH and PCB even more

[pvit]

Reworked everything . There were a lot of experiments, but here is only final [almost] version:



Bottom:



Bigger working area, better look. Now enough for 99.9% of hobby projects .

I also documented details of assembly process on github: https://github.com/puzrin/reflow_micro/blob/master/doc/heater_assembly.md. Photos are a bit old, already switched to aluminium plates and simplified technology. Hope to finish experimenting next week and will update docs to final version.

[pvit]

Made more heaters with plates of different thikness, to test temperature difference. Thermal camera shows only general picture, so used K-thermocouple via drop of rose metal to check most hot (~ center) and most cold (corner at wires side) points. Checks have been done at medium (~ soaking) and high (~ peak) temperatures.

4mm:

- medium: 176-181°C, Δ = 6°
- high: 263-271°C, Δ = 8°

3mm:

- medium: 184-191°C, Δ = 7°
- high: 272-282°C, Δ = 10°

2mm:

- medium: 163-170°C, Δ = 7°
- high: 269-282°C, Δ = 13°

As conclusion - 4mm plate is good for any cases. It still can be cooled fast enouth with fan.

Pictures of winner: